Mass spectral study of O- and S-aryl dimethylthiocarbamates under electronimpact conditions: Newman-Kwart rearrangement in the gas phase

The electron impact (El) mass spectra of isomeric S- and O-aryl (2-naphthyl , R-Ph- = aryl, where R = H, NO2, COOCH3, COCH3 and OCH3) dimethylthiocarba mates have been studied in detail. The El spectra of O-aryl dimethylthiocar bamates include some of the fragment ions that are characteristic of the co rresponding S-aryl isomer, which could be explained by a Newman-Kwart rearr angement in the ion source of the mass spectrometer, after ionization. The El mass spectra of S-aryl dimethylthiocarbamates showed specific fragment i ons resulting from cleavage of the molecular ion involving the bond between sulfur and the carbonyl group of the carbamate moiety (alpha -cleavage). T he EI mass spectra of O-aryl dimethylthiocarbamates, however, showed the fr agmentation of the molecular ion by alpha -cleavage involving the bonds on both sides of oxygen atom. Further, the El mass spectra of O-aryl dimethylt hiocarbamates containing an electron-withdrawing substituent (-R) on the ar yl group showed a characteristic fragment ion corresponding to [M - R](+). Copyright (C) 2001 John Wiley & Sons, Ltd.